Iodine

Energy Metabolism T3 T4 Seaweed Thyroid Iodine Pregnancy Mineral Trace Element Iodide Hypothyroidism Goiter Thyroxine Weight Management Fetal Development Cretinism Selenium Kelp Bladderwrack Iodized Salt Hashimoto's Graves' Disease Thyroid Hormones

Published on December 20, 2025 by Guy

Iodine is an essential trace mineral with a singular, vital function: it is required for the production of thyroid hormones thyroxine (T4) and tri-iodothyronine (T3), which regulate metabolism, energy production, and body heat. Found primarily in seafood, seaweed, and iodized salt, deficiency remains common worldwide, particularly in inland and mountainous regions. While adequate iodine supports energy, metabolism, and healthy skin/hair/nails, both deficiency and excess can cause thyroid dysfunction and goiter—making proper dosing essential.

Effects and Benefits

Core Identification

Common Names:
- Iodine
- Iodide (compound form used in supplements and fortified salt)
- Potassium iodide (KI)
- Sodium iodide

Latin Name: N/A (Chemical element: I)

Category: Mineral (Essential Trace Element)

Uses

Traditional Uses

  • Goiter prevention and treatment - Global medical practice, 1920s onwards (following discovery of iodine's thyroid role)
  • Thyroid support - Traditional use of seaweed consumption in coastal cultures (Japan, Ireland, coastal communities)
  • Antiseptic wound care - Western medicine (topical iodine solutions, not for internal use)

Modern Uses

  • Hypothyroidism (iodine-deficiency type) - Thyroid hormone support | Research quality: Strong
  • Key findings: Iodine is essential for producing T3 and T4 thyroid hormones. Deficiency leads to reduced hormone production, causing fatigue, weight gain, cold sensitivity, dry skin, brittle hair/nails, and mental sluggishness. Supplementation can reverse these symptoms when hypothyroidism is caused by iodine deficiency. Selenium plays a role in thyroid hormone metabolism, and effects of iodine deficiency are worsened by low selenium intake.

  • Source citations: Brewer - TDT Encyclopedia of Vitamins; Merck Manual; Weil - Eating Well for Optimum Health

  • Goiter prevention and treatment - Thyroid gland normalization | Research quality: Strong

  • Key findings: Both deficiency and excess iodine can cause goiter (thyroid gland enlargement). In deficiency, the gland swells attempting to capture more iodine. Iodized salt programs have largely eliminated endemic goiter in developed nations. Worldwide, iodine deficiency remains the most preventable cause of mental retardation and developmental issues.

  • Source citations: Merck Manual; Brewer - TDT Encyclopedia of Vitamins

  • Pregnancy and fetal development - Preventing cretinism and developmental defects | Research quality: Strong

  • Key findings: Adequate iodine during pregnancy is critical for fetal brain development. Deficiency increases risk of miscarriage, stillbirth, and birth defects. Infants born to iodine-deficient mothers may develop cretinism (severe mental retardation with short stature) if not treated soon after birth. Treatment must be given before the sixth month of pregnancy to protect fetal brain development.

  • Source citations: Brewer - TDT Encyclopedia of Vitamins; Merck Manual; Cordain - The Paleo Answer

  • Metabolic support - Weight management assistance | Research quality: Preliminary

  • Key findings: Sub-optimal iodine intake may contribute to feelings of lethargy and difficulty losing weight in people whose thyroid hormone levels are in the low-normal range. Iodine is included in many weight loss products as a mild thyroid stimulant. Most effective when actual deficiency is present.
  • Source citations: Brewer - TDT Encyclopedia of Vitamins

Active Compounds

Primary Active Ingredients:
- Iodine/Iodide - The essential element used by the thyroid gland to produce T3 and T4 hormones; iodide is the ionic form absorbed from food and supplements

Dosage Information

Standard Dosage (Recommended Daily Allowance):
- Form: Iodized salt, kelp tablets, or multimineral supplement
- Amount: 150 mcg per day (adults)
- Frequency: Daily, typically obtained through diet

Therapeutic Dosage:
- Form: Kelp, bladderwrack, or iodine supplement
- Amount: 150-300 mcg per day
- Purpose: Addressing mild deficiency or supporting thyroid function
- Duration: As needed; monitor thyroid function if using long-term
- Note: Limit total iodine to no more than 300 mcg daily from food and supplements when autoimmune thyroid conditions are present

Maximum Safe Dosage:
- Daily maximum: Do not exceed 1,100 mcg (1.1 mg) per day from all sources without medical supervision
- Warning threshold: High-dose iodine supplements (>150 mcg daily) can paradoxically suppress thyroid function or worsen Hashimoto's thyroiditis
- Athletes: May need more iodine as significant amounts are lost through sweat—an athlete in heavy training can lose the full 150 mcg RDA in sweat alone

Bioavailability Notes:
- Iodine is well absorbed from both food and supplements
- Iodine from kelp and seaweed sources provides naturally occurring trace minerals alongside iodine
- Up to 3% of people are allergic to iodine; long-term use of kelp supplements can cause sensitivity reactions

How to Take It

Timing:
- Best time of day: Morning or with meals
- With food or on empty stomach? May be taken with or without food
- Specific timing notes: Consistent daily intake is more important than specific timing

Synergies - What It Works Well With

Complementary Supplements:
1. Selenium - Essential cofactor for thyroid hormone metabolism | Selenium helps convert T4 to active T3 and protects thyroid tissue from oxidative damage; deficiency of both minerals worsens thyroid dysfunction
2. Zinc - Supports thyroid hormone production | Both zinc and selenium deficiency can contribute to hypothyroidism
3. Vitamin A - Supports iodine utilization | Vitamin A deficiency can reduce the thyroid's ability to assimilate iodine and contribute to goiter
4. Tyrosine - Amino acid precursor to thyroid hormones | L-tyrosine (500 mg twice daily) is converted into T3 and T4 in the body

Avoidance - What NOT to Combine With

Supplement Interactions:
1. High-dose selenium - While moderate selenium supports iodine function, excessive selenium combined with iodine may overstimulate the thyroid

Drug Interactions:
1. Thyroid medications (Synthroid, Levothyroxine, Armour) - Iodine supplementation may interfere with thyroid hormone medications; requires medical supervision | Severity: Moderate to Severe
2. Lithium - Both lithium and high-dose iodine can suppress thyroid function; combination increases risk of hypothyroidism | Severity: Moderate
3. Amiodarone - This heart medication contains high amounts of iodine and can cause thyroid dysfunction; additional iodine supplementation not recommended | Severity: Moderate
4. Anti-thyroid medications (Methimazole, PTU) - Iodine can interfere with the action of drugs used to treat hyperthyroidism | Severity: Moderate

Food Interactions:
- Goitrogenic foods in excess - Large amounts of raw cruciferous vegetables (cabbage, cauliflower, broccoli, kale, Brussels sprouts, turnips), millet, peanuts, and soy can inhibit iodine uptake by the thyroid; effect is minimized by adequate iodine intake or cooking these foods
- Soy isoflavones - May impair iodine metabolism and thyroid function, particularly concerning during pregnancy or in infants fed soy formula

Safety Information

Contraindications:
- Hashimoto's thyroiditis - High-dose iodine can aggravate this autoimmune condition
- Graves' disease (hyperthyroidism) - Excess iodine can worsen hyperthyroid symptoms
- Known iodine allergy (approximately 3% of population)
- Autonomous thyroid nodules

Side Effects:
- Common: Metallic taste in mouth with excess intake
- Uncommon: Oral sores, headache, skin rash
- Rare: Iodine fever (at very high doses of 50-500 mg/day), allergic reactions including edema, eosinophilia
- Paradoxical effect: Both deficiency AND excess can cause goiter and thyroid dysfunction

Long-Term Use:
- Safety of prolonged use: Generally safe at RDA levels (150 mcg/day); long-term high-dose use not recommended
- Monitoring recommendations: Thyroid function tests (TSH, T3, T4) recommended if supplementing above RDA for extended periods
- Cycle recommendations: Continuous use is acceptable at dietary levels; higher therapeutic doses should be monitored

Special Precautions:
- Pregnancy: Adequate iodine is critical (220 mcg/day recommended); both deficiency and excess are harmful to fetal development. Pregnant women with borderline iodine status who consume high-soy diets may become deficient.
- Lactation: Increased requirement (290 mcg/day recommended)
- Infants: Those with congenital hypothyroidism on thyroid medication must not have soy formula amounts changed without consulting a pediatric endocrinologist
- Elderly: Monitor thyroid function as sensitivity to iodine changes with age
- Pre-existing thyroid conditions: Consult healthcare provider before supplementing

Primary Uses At-a-Glance

Primary: Thyroid support, goiter prevention, hypothyroidism (iodine-deficiency type), pregnancy/fetal development support, metabolism support

Secondary: Energy support, healthy skin/hair/nails, mental clarity, weight management support (when deficiency is a factor)

Sources

Local Library:
- Brewer, Sarah - TDT Encyclopedia of Vitamins
- Merck - The Merck Manual Home Health Handbook
- Mars, Brigitte - The Country Almanac of Home Remedies
- Weil, Andrew - Eating Well for Optimum Health
- Brighten, Jolene - Beyond the Pill
- Bellebuona, Holly - An Herbalist's Guide to Formulary
- Cordain, Loren - The Paleo Answer
- Lust, John - The Natural Remedy Bible
- Moyad, Mark - The Supplement Handbook
- Bone, Kerry - A Clinical Guide to Blending Liquid Herbs
- Gaby, Alan R. - A-Z Guide to Drug-Herb-Vitamin Interactions

General Knowledge:
- Institute of Medicine (IOM) Dietary Reference Intakes
- National Institutes of Health (NIH) Office of Dietary Supplements